The early mapmakers really had it very hard to create a proper map, as they didn't had any of the modern technology that nowadays we do. They had to rely on their orientation in the space, be able to properly adjust the distances, using only their eyes and brains. Also, they were putting into the maps areas that were told and described by them by people that were there, but they personally haven't even seen the place. The knowledge they had about the size of the world was very limited, as they were not really able to travel that much during their lifetime.
Their interpretation is usually relatively good and relatively accurate considering the circumstances. Of course there were some misjudged distances and proportions, but not by far. Since they only new so much of the world, they usually were making the map, thus the size of the world, from the eastern most location they new, to the westernmost location they new, either putting straight lines like that is the end of the world, or putting waters to mark the same.
